Rheostat switch



Patented Oct. 17, 1950 EHEOSTAT SWITCH Earl C. Booth, Columbus, Ind.,assignor to Arvin Industries, Inc., a corporation of Indiana ApplicationAugust 23, 1948, Serial No. 45,703

3 Claims.

This invention relates tc a combined switch and rheostat of the typesuitable for controlling the operation and speed of small electricmotors. It is the object of the invention to produce a switch which canbe simply and economically manufactured and which will be compact andadaptable for installations where a small amount of space is available.

In carrying out the invention, the body of the switch is formed as asheet-metal stamping having a base, opposed side walls, and an end wall.A plate of insulating material about which a resistance element iswrapped overlies the edges of the side walls and is secured thereto.Such plate also bears a stationary switch contact to which a terminaland one end of the resistance element are connected. The body of theswitch constitutes the other terminal, and its end wall is provided withan exteriorly threaded sleeve serving both as a mounting means for theswitch and as a guide for a longitudinally slidable operating rod havingsecured to its end a U-shaped member of resilient material one lef.r ofwhich bears against the body-base and the other leg of which ispositioned to engage the stationary contact and the successive turns ofthe resistance element as the rod is moved longitudinally of itself.

In the accompanying drawing, which illustrates the invention, Fig. 1 isan elevation of the switch; Fig. 2 is a section on the line 2-2 of Fig.1'; Fig. 3 is a section on the line 3-3 of Fig. 2; and Fig. 4 is asection on the line 4 4 of Fig. l.

The switch shown in the drawing comprises a body formed as a sheet-metalstamping to have a base I Il, side walls II, and an end wall I2. The endwall is provided with an opening which receives an end portion ofreduced diameter on an exteriorly threaded sleeve I3, thereduced-diameter end portion of the sleeve I3 being riveted over asindicated at I4 to secure the sleeve rigidly to the end wall I2. Nuts I5on the sleeve complete a means for mounting the switch.

Overlying the edges of the side walls Il is a rectangular plate I'I ofinsulating material having in its opposite edges a series of notcheswhich receive and locate successive turns of an electrical resistancewire I8. One end of the resistance wire I8 is formed into an eye I9which limits the extent to which the wire can be drawn through a holelocated in the plate I'I between the side walls II of the body. Fromsuch hole, the wire is wound about the body for several turns and isanchored at its opposite end beneath the outer head of a rivet 20, whichalso serves to secure to the plate Il a terminal 2l adapted forconnection to an electrical conductor 22. Desirably, the notches in theedges of the plate I'I are so located and the wire so disposed in themthat those stretches of wire on the inner face of the plate I1 willextend in a direction normal to the edges of such plate.

The plate II is desirably located on the switch body by having in itsside edges notches which receive fingers 24 on the side walls II of theswitch body. After the plate is in place on the switch body, the fingers24 are bent over the plate as indicated in Figs. 1 and 4 to hold theplate securely in place. Over the region occupied by the inner stretchesof the resistance wire I8, the side walls II of the switch body arenotched, as shown at 25 to prevent electrical contact between theresistance wire and the switch-body. Additional notches 26 are desirablyprovided in the side wal-ls I I adjacent the end wall I2. The notches 25and 26 and the open end of the switch-body opposite the end wall I2permit free access of air to the interior of the switch-body and henceare of value in providing for cooling of the resistance wire I8 when theswitch is mounted in close quarters.

The switch is operated by a rod 30 longitudinally slidable in the sleeveI3 and provided at its outer end with an operating knob 3|. To the innerend of the rod 30 there is secured the intermediate leg of a U-shapedstrip of resilient material 32, which serves as a means for electricallyconnecting the switch-body with the rivet 20 or with any of the turns ofthe resistance wire I8. For this purpose, the outer leg of the strip 32is provided with an outwardly offset portion or contact 33 which, bymovement ofthe rod 3U, can be shifted from a position beyond the rivet20 into engagement successively with the inner head of such rivet andwith the Several turns of the resistance wire I8.

Desirably, the contact 33 is so dimensioned that it can enter for ashort distance into spaces between adjacent turns of the resistancewireI8 in order that it will act as a detent releasably holding the rod 30in any of a series of definite longitudinal positions. To locate thecontact 33 in engagement with the inner head of the rivet 20 and also tolocate it in the off position beyond such rivet-head, the inner leg ofthe strip 32 is provided with offsets 35 releasably engageable withdepressions 36 formed in the base II) of the switch-body.

The terminal 2l is shown in the drawing as of Lshape, but it may haveother forms. It includes a portion which lies against the outer face ofthe plate i7 and is provided with an inwardly bent nger 3S adapted to bereceived in an opening 39 in the plate l to prevent the terminal fromrotating about the axis of the rivet 2Q. Conveniently, the opening 39 isformed by a punching operation which is not carried to completion, withthe result that the slug EB is left in the openinff 39 and projectsinwardly of the switch-body to receive and support the mov-v ablecontact 33 when the switch is in the ofi position and to prevent suchcontact from engaging the finger 3S.

When the switch is used in an automobile, as for the purpose ofcontrolling the operation and speed of an electric motor associated withan automobile heater', it is conveniently mounted in a ange #i9 such asis commonly provided along the lower edge of a metal instrument panel Tomount the switch, the nange "i5 is provided with an opening large enoughto roccive the sleeve I3, the outer nut l5 is removed from the sleeve,the sleeve is inserted through the opening from above, and the lower nutis replaced and tightened to clamp the switch firmly in position. A sthe switch-body is grounded through engagement of the sleeve i3 with thegrounded instrument panel i, he switch controls the connection of theconductor to ground either directly or through one or more turns of theresistance wire I3. The two legs of the strip 32 bear oopositely andwithsubstantially equal force inst the body-baie El? and the elementscarried by the plate I7 with the result that no lateral forces of anyappreciable magnitude are applied to the inner end or" the rod which istherefore free to slide without binding in the sleeve i3.

I claim as my invention:

1. A combined switch and rheostat, comprising a unitary metal bodyhaving a base, opposed side walls, and an end wall, a plate ofinsulating material secured to said side walls in spaced relation to thebase, a fixed contact secured to said plate, a resistance wire wrappedabout said plate with its turns in spaced relation and one of its endsconnected to said fixed Contact, a terminal secured to said iixedcontact, a rod supported from said end wall for sliding movement betweenthe base and plate, and a generally U-shaped strip of resilient materialhaving its intermediate portion secured to said rod with one of its endsbearing against the base and the other in position to engage the fixedContact and successive turns of the resistance wire as the strip isshifted in movement of the rod, said strip being formed of electricallyconducting material to provide a direct path for electric currentbetween the point at which one of its ends engages said base and thepoint at which its other end engages a turn of said resistance wire.

2. A device as set forth in claim 1 with the addition of a sleevesecured to said end wall and projecting outwardly therefrom, said rodbeing slidable in said sleeve, said sleeve being exteriorlyscrew-threaded, and nuts on said sleeve for clamping the switch to amounting member.

3. A device as set forth in claim 1 with the addition that the sidewalls of the switch-body are provided with notches between the end walland the adjacent end of the plate and with additional notchesccextensive with that portion of the plate about which the resistancewire is wrapped.

EARL C. BOOTH.

cnFE-ENCES CXTED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

